“Can you spy him deep within? Little Possum. Black as sin.” That’s just part of the creepy children’s poem that accentuates the sheer bloody terror in Possum, a supremely disturbing British horror flick from writer-director Matthew Holness, creator of Darth Marenghi’s Darkplace.

Based on Holness’ own short story, Possum stars Sean Harris as Philip, a disgraced children’s puppeteer who returns to his childhood home with a suspiciously large leather bag. Inside the bag is Possum, perhaps the scariest puppet ever committed to celluloid. The frankly terrifying poster for the film (google it at your peril) gives some idea of the horror, but the finished article is guaranteed to give you nightmares for weeks.

On the surface, the plot is deceptively simple: Philip repeatedly tries to destroy the puppet, only to find that it keeps coming back. Is it all in his mind? Or is Possum actually…alive? At the same time, Philip finds his attempts to put his troubled past behind him actively hampered by the presence of his malevolent stepfather, Maurice (Alun Armstrong).

Opening Possum with a 1970s-style credits sequence and shooting on 35 mm, Holness conjures a suitably unsettling, grimy aesthetic where menace lurks in every shadow. On top of that, Holness knows exactly what to put in those shadows to maximise the terror, often sneaking in just a flicker of movement in the darkness at the last second, so you hope to god you didn’t just see what you thought you saw. In that respect, the film often recalls Eraserhead in its mastery of pure nightmare imagery. It’s also strangely beautiful in places, as illustrated by an early shot of red and yellow balloons being slowly enveloped in black smoke, a shot that’s simultaneously haunting, sinister and yet oddly pleasing.

Formally, the film is commendably daring and unlikely to be to everyone’s taste. It’s slow moving and frequently repetitive, but both of those devices serve to draw you in deeper, creating illusions of safety that will soon be shattered. Similarly, the film unfolds with minimal dialogue for the most part, only to hit you with some of the most terrifying words you’ve ever heard – one sentence in particular will stay with you a very, very long time.

On top of that, Possum makes brilliant use of the children’s poem in a way that recalls The Babadook, where the haunting, child-like imagery and words of the children’s story were actually a metaphor for something much darker. Here, the poem works in conjunction with the already terrifying puppet, and the film feeds you the lines in such a way that you start to dread what might happen when it comes to an end.

Harris is superb as Philip, his perpetually haunted features making him look he’s terrified of his own inner darkness, and maybe with good reason. Similarly, Armstrong delivers a performance that’s so profoundly disturbing that you’ll never look at the actor quite the same way again.

Put simply, Holness’ dark and disturbing debut feature will scare you silly, to the point where you’re actually afraid to close your eyes at night, in case you start dreaming about Possum. After all, “Possum with his black balloons, will eat you up in bed…”